1. Field of the Invention
This invention relates generally to a thin-gauge composite material formed of layers of specialized carbon fibers and polymeric resins and, more particularly, to a composite carbon fiber material that is useful in an electrical contact assembly typically used in an electromechanical device.
2. Description of the Background
The use of carbon fiber material for structural applications is well known. Typically, this material is composed of multiple layers of either woven fabric or layers of unidirectional, continuos carbon fibers that are laminated together. The orientation and number of layers are chosen to meet the stiffness, strength, and dimensional stability requirements of the particular application. In typical aerospace applications the thin gauge material has between four to eight plies, with a thickness in the range of 0.030 to 0.060 inches. Various processing methods for applying heat and pressure to consolidate the layers of the carbon fiber reinforced thermoplastic and thermosetting composites include the use of autoclaves, presses, and pultrusion. These carbon fiber materials can be formed or shaped by stamping, cutting and machining. The thermoplastic composites can be successively processed, for example, consolidation can be followed by forming and welding. Although thin-gauge composite materials exist, they are not suitable for microelectronic applications presently under consideration.
In U.S. patent application Ser. No. 09/498,872, assigned to the assignee of this application and the disclosure of which is incorporated herein by reference, it is proposed that an electrical contact be formed of carbon fibers that are arranged in a side by side fashion and embedded in an electrically conductive matrix. Nevertheless, both the electrical characteristics and the mechanical characteristics of this carbon fiber electrical contact are seen to be subject to improvement.
Therefore, the need arises for improvements in carbon fiber materials.
Accordingly, it is an object of the present invention to provide an improved carbon fiber composite material that has similar mechanical properties as existing composites but with a smaller thickness, as well as providing good electrical conductivity, and in which the material is a composite formed of carbon fiber materials and elastomeric resin layers.
It is another object of the present invention to provide a composite carbon fiber material having a layer of aligned carbon fibers that has arranged on both flat sides thereof a nonwoven carbon fiber mat, woven fabric or off-axis unidirectional layers with the outer surfaces of the carbon fiber mats being finely coated with a polymeric resin.
A further object of the present invention is to provide a composite carbon fiber material having multiple layers of the carbon fibers that are aligned in a polymeric matrix and adhered together with the multiple layers then being laminated with mats formed of nonwoven carbon fibers, woven fabric or off-axis unidirectional layers, with the exterior surfaces of the mats being coated with a polymeric resin for forming the composite material into a stable structure.
In accordance with one aspect of the present invention the carbon fibers that are aligned and bound in a polymeric matrix are combined between two nonwoven carbon fiber mats, woven fabric or off-axis unidirectional layers. The nonwoven carbon fiber mats, woven fabric, or off-axis unidirectional layers provide improved mechanical strength and stability to the aligned carbon fiber layer and also provide a primary current carrying capability to aid in the overall electrical conductivity of the composite material. Unidirectional electrical conductivity can be achieved by using two methods: carbon fiber to carbon fiber contact between the individual layers that is applicable to both non-conductive and conductive polymers; and/or by adding conductive materials to the resin layer or layers. The fabrication techniques utilized in making the composite material create a network of connections between the differently oriented carbon fibers to provide the desired electrical conductivity. The extent of this conductivity is regulated by the resin volume fraction and may be increased by introducing conductive particles into the resin layer or layers of the composite.
The unidirectional carbon fiber layer is used for carrying electrical current along a primary axis as well as creating mechanical stability along that axis. Used alone, however, this material provides no off-axis electrical conductivity and has virtually no off-axis mechanical stability. The present invention teaches the use of a nonwoven fabric, woven fabric and off-axis unidirectional layer of carbon fibers to provide off axis current carrying capabilities, as well as adding off-axis mechanical stability.
The layer or layers of resin provide additional bonding material for the additional carbon fiber layers and control the overall composition of the material. By varying the ratio of insulative resin to carbon fiber, the mechanical and electrical properties of the composite can be tailored to meet a variety of applications. Also, by introducing and varying the ratio of conductive particles to the resin layer or layers the total electrical conductivity can be increased to be above that which can be achieved by the network of carbon fibers alone.
The invention can contain one or more layers of each of the above-described components depending on the desired electrical and mechanical properties specified and the material layering pattern may be changed depending on the application requirements. By using the above layers of carbon fibers and elastomerics, the resulting composite material can be fabricated at a thickness of less than 0.010 inch.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof to be read in conjunction with the accompanying drawings.